Every new OS X release has its own special challenges, and OS X 10.11 - which I still have trouble referring to as "El Capitan" - is no different. And in our testing (which we commenced immediately upon availability of the developer preview), we found that we couldn't make a copy of an El Capitan disk due to the new system protection or rootless feature.

Rootless mode is a good thing, for the most part. It makes OS X more secure by protecting various system folders, ensuring that even applications that obtain escalated privileges through trickery (or hacking) can't mess with these critical locations. (It also means that jailbreaking iOS 9 is likely to be much more difficult, for those who care about that kind of thing.)

In our investigation, we've found that a new Extended Attribute -- com.apple.rootless -- is used to mark files and folders with this new protection. No process other than certain Apple-signed-and-authored ones can remove or write this attribute, and files and folders marked with this attribute cannot be changed. However, those files and folders can be read and copied.

This means that, for those using El Capitan, we can't hint obliquely that we're compatible, as we have in the past, where our current version worked even though we couldn't declare that compatibility until the final build. This time, the current version of SuperDuper is dead in the water on El Capitan. It just won't work.

But don't dismay: we've worked to change that. I'm happy to say, to those of you who are on the Beta (and those who are going to join the public beta today), we've developed and tested a Beta version of SuperDuper that makes bootable copies of El Capitan. There's a link to download it at the end of this post.

But please don't skip down there. Keep reading.

There are a few minor caveats, and some things to keep in mind.

First, and most importantly, OS X 10.11 is in Beta, and so is this build of SuperDuper. While we've been super careful about changing as little as possible, El Capitan is a big update, and there may be things that don't work. There may be things that don't work as well as you'd like. If that's the case, report the problem to the appropriate party. We're happy to get the feedback, and I'm sure Apple is as well.

Operationally, there are some known, minor issues. The most inconsequential one is that Repair Permissions is no longer available under El Capitan, so we disable it in Options. I can't say it will be missed.

Since we can't write the com.apple.rootless EA, SuperDuper removes it during the copy. That means the backup -- while fully functional and bootable -- is not an "exact copy" of the source. Specifically, SuperDuper! must disable the system protection feature on the backup, and cannot recreate it when you restore.

That's a relatively minor difference, but it's an important one. After restore, your system becomes vulnerable to the kinds of attacks that Apple is specifically protecting against.

It's easy to regain full system protection features: you simply need to reinstall the OS from the App Store. You can do this at your leisure, but doing it as soon as possible means you're less vulnerable (even though that vulnerability is quite small). It's a painless process, and it writes the fresh OS under your existing applications and data. As an added benefit, it will speed up your boot process, since it'll recreate certain caches that non-special-Apple-programs can no longer update.

Also, for this version, if you want to restore over an existing El Capitan install, and there are changes in protected system folders, you cannot use Smart Update (because we can't overwrite those protected files, or write to those protected folders). We're hoping to remove this restriction in the next release.

That's it for now! Thanks, as always, for using and recommending SuperDuper: we appreciate it, and couldn't do it without your support.